1. Field of the Invention
The present invention relates to a semiconductor device, and particularly, is suitably applicable to a semiconductor device including a diode as a protection element.
2. Description of the Background Art
In a semiconductor device, a protection element is formed in order to prevent a specific element from being destroyed by a surge, static electricity or the like. One of such protection elements is a diode referred to as a FID (Full Isolation Diode). This type of semiconductor device is disclosed in Japanese Patent Laying-Open Nos. 10-74958 and 11-121768.
In such a semiconductor device, a P-type epitaxial growth layer is formed on a P-type semiconductor substrate with an N-type buried region and a P-type buried region interposed therebetween. In this P-type epitaxial growth layer, a cathode region (N-type) and an anode region (P-type) are formed at a distance from each other. Also, an N-type sinker region penetrating the P-type epitaxial growth layer to the N-type buried region is formed.
In this semiconductor device including a diode, the N-type sinker region is electrically connected to the N-type buried region and electrically connected (short-circuited) to an anode region of the diode, thereby achieving an effect of suppressing a leakage current flowing from a cathode region to the semiconductor substrate.
However, when a surge or the like flows into the semiconductor device, a current resulting from such a surge may flow into both of the semiconductor substrate and the cathode region. At this time, the operation of the parasitic PNP transistor causes a current to flow from the semiconductor substrate into the anode region, and also, the current having flown into the anode region acts as a base current of the parasitic NPN transistor, so that the operation of the parasitic NPN transistor is accelerated. Consequently, a large current flows from the cathode region through the N-type buried region into the N-type sinker region, which may finally result in destruction of the diode.
Thus, in semiconductor devices, countermeasures for preventing such destruction of the diode have been taken by electrically connecting a resistance element to an anode region, thereby suppressing the operations of the parasitic PNP transistor and the parasitic NPN transistor.